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Presentation on theme: "Houston…we have a problem 1) You learned that if you push on a door far away from it’s hinges (the axis of."— Presentation transcript:

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Houston…we have a problem http://www.youtube.com/watch?v=eco_xvkEQlg 1) You learned that if you push on a door far away from it’s hinges (the axis of rotation) it will be easier to open and close 2) You learned if you hang a mass farther away from your hand (the axis of rotation) it was harder to move up and down Don’t they contradict one another?

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So what exactly did we learn? The direction that you apply the force is rather important If you apply your force in the same direction as the object moves… less effort is needed with a longer lever If you apply your force opposite the direction that the object moves…more effort is needed with a longer lever

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What is torque? Torque is a tendency of a force to rotate an object about an axisforce A force applied to an extended object can produce a torque. This torque in turn causes the object to rotate.

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The object rotates about an axis. The lever arm is the distance (in meters) from the axis of rotation to the point where the force acts. The applied force is the force applied to the lever arm.

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Calculate using equilibrium A boy and his cat sit on a seesaw. The cat has a mass of 4 kg and sits 2 m from the center of rotation. If the boy has a mass of 50 kg, where should he sit so that the see-saw will balance?

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A boy and his cat sit on a seesaw. The cat has a mass of 4 kg and sits 2 m from the center of rotation. If the boy has a mass of 50 kg, where should he sit so that the see-saw will balance?

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Less force is required farther out from the center of mass than closer in. So, by tackling a runner low -- far from the center of mass -- it takes less force to tackle him than if he were tackled high. Furthermore, if a runner is hit exactly at his center of mass, he will not rotate, but instead will be driven in the direction of the tackle. Similarly, coaches often advise linemen to stay low. This brings their center of mass closer to the ground, so an opposing player, no matter how low he goes, can only contact them near their center of mass. This makes it difficult for an opposing player to move them, as they will not rotate upon contact. This technique is critical for a defensive lineman in defending his own goal in the "red" zone, the last 10 yards before the goal line.